What I am trying to do:
Using old cellphones/tablets as digital photo frames, or screens for monitoring PC/network.
How I am trying to do it:
Using the original li-ion battery protection board and running 4.0VDC through it to power the cellphone/tablet.
Results so far:
Mixed. Occasionaly it works, most time it doesn't.
What I've done/learned so far:
So I'm trying to have some cellphones/tablets powered up and running 24/7, and I know just leaving the li-ion battery in the device and having it plugged into a USB charger all the time is NOT good for the battery, and could eventually lead to killing the li-ion battery in a flashy, sparkling, destructive manner. Since I want to avoid that at all cost, I want to power the cellphone/tablet device without the li-ion battery. Most modern cellphones/tablet will have a li-ion battery that has it's own protection board attached to it, so hooking up a 4VDC source straight to the devices' positive and negative voltage inputs will not power up the device because there is no li-ion protection (control?) board attached and communicating with the device. So I've removed said protection (cotrol?) board from an original OEM battery and tried to feed the 4VDC through the board into the cellphone/tablet with very mixed results.
1. It won't power up the device if the board is placed into the device first, then power is applied. Power must be applied first to the board, then the board placed in the device. However, even with that...
2. Half the time if the device powers up, it'll boot like normal, get into the OS and main GUI, then shut off as if it lost power. Sometimes when this happens, it'll start going through a reboot/shutdown loop, as if it's experiencing a brown out every time, but I know that voltage supply I am providing can supply more amperage then the device could need (I've only measured around 1.2A spikes @ 4V, and the power supply can easily deliver 3A+).
3. The times I have gotten it to power on and stay on, the voltages detected by the OS (Android) are way off from the actual supplied voltage. To me, it seems the li-ion protection board is ignoring the actual voltage on the "battery" side, and going by some internal counter on how much battery capacity has been used or recharged. Using a power supply with a fairly solid 4.0VDC output even under load, the voltages displayed by the Android system are all over the place. Using 18650 batteries, the Android will detect voltages totally different then the actual battery voltage. I even tried charging the 18650 battery through the cellphone, and when the Android OS indicated 100% charge, it was reading 4.385V, while the actual 18650 battery was only 3.874V measured.
I really want to use these old cellphone/tablets, but cannot figure out a reliable way to power the device because of the control board. I thought it would as simple as just supplying 3.8-4.0V, but I've only had bad results so far. I've tried searching for anything battery related to getting devices powered without a li-ion battery to no avail. I'm hopeing someone with experience in doing so could point me in the correct direction to get this working.